This invention is directed to a scavenging medical hood for removal of residual aerosolized medicinal agent from respiratory gas passed through the hood.
A variety of medicinal agents are administered as aerosol sprays to patients in need thereof. Generation of the aerosol spray is accomplished via one of many commercially available nebulizers.
For adults and older children hand held nebulizers are used for short term or single dose therapy of an aerosolized medicinal agent. These hand devices are not suitable for use with small children or infants since they require cooperative breathing of the patient.
Aside from intubation, if long term administration of an aerosolized medicinal agent is necessary, or if it is necessary to administer a medicinal agent to a severely compromised adult or older child as, for instance, a comatosed patient, and in all instances for administration to young children and infants, administration is accomplished utilizing a hood or tent.
Various hoods and tents (oxygen tents) are commercially available for the administration of oxygen and other respiratory gasses to patients in need thereof. A typical hood or tent utilized as an enclosure for respiratory therapy has to accommodate a patient who normally is in a prone position in a bed, crib or the like. The enclosure must therefore seal against normal bedding, as for instance, sheets, blankets and pillows. Inherently these seals are not imperforate. Aside from spark and flame arrestment, during normal oxygen therapy this does not present any problems since leakage at such imperfect seals only constitutes enrichment of the oxygen in the ambient atmosphere around the outside of the enclosure.
Respiration involves the exchange by the patient of carbon dioxide for oxygen. Because of biological feedback mechanisms wherein the concentration of the carbon dioxide affects the breathing of the patient it is necessary to purge carbon dioxide from the respiratory gasses inhaled by the patient. This, thus requires a continuous flow of respiratory gas into a suitable hood or tent with the volume of the input gas sufficient to essentially flush the respiratory environment within the hood or tent of carbon dioxide. Normally a positive gas flow is established through the hood or tent with the excess gas flow discharged directly to the ambient environment.
An aerosolized medicinal agent can be administered via a hood or tent by simply introducing the output of a nebulizer into the input gas stream of the hood or tent. In a simplistic sense the humidification of oxygen gas fed to an oxygen tent can be considered as such a system. In this case the water vapor introduced to the oxygen stream could be equated as a medicinal agent serving to the humidify the air for facilitation of respiration of the patient. As with the discharge of oxygen, discharge of excess water vapor to the ambient air whether via an outlet port of the tent or via leakage from imperfect seals does not constitute an environmental problem.
When medicinal agents are added to the respiratory gasses of a hood or tent, sufficient medicinal agent must be added to the gasses to account for the continuous flushing of excess gas through the hood or tent. In the water vapor example discussed above, excess medicinal agent discharged from a tent or hood, i.e. the water vapor, is completely benign once it is exhausted from the hood or tent. In other cases, however, it is desirable not to vent excess medicinal agent to the ambient environment external of the hood or tent.
Attempts have been made to purge tents or hoods of excess medicinal agent. The basic premise of all of these attempts is the connection of a vacuum system directly to the interior of the hood or tent. The vacuum system is then used to remove gas containing excess or residual medicinal agent prior to the expulsion of the same to the ambient environment.
The use of such direct vacuum removal of excess or residual medicinal agent from the interior of a respiratory device such as a hood or tent, has only been marginally successful. This is because equilibrium must be established and maintained between the flow rate of gasses into the enclosure against the vacuum exhaust of gasses from the enclosure.
Establishing and maintaining gas flow equilibrium is difficult. If there is a net positive pressure within the interior of the enclosure, i.e. the flow rate into the hood or tent is greater than the vacuum flow rate out, excess gas and medicinal agent contained therein will leak from the enclosure, as for instance, around bed sheets, draped seams and the like. If there is a net negative pressure, i.e. the vacuum flow rate is greater than the respiratory gas input flow rate, the concentration of the respiratory gasses and/or the medicinal agent suspended therein will be diluted by ambient air which will be drawn into the enclosure through the very same inefficient seals around bed sheets, draped seams and the like. Even when equilibrium is established if, for instance, the patient moves disturbing the seal of the enclosure against beds, sheets, pillows or the like, the equilibrium can be disrupted.
Thus, to establish and maintain equilibrium in a vacuum removal system either very complex and thus very expensive monitoring equipment must be utilized or constant attention by medical personnel is required to continuously adjust the flow rates.